Ordinarily, a tape cassette rotatably accommodates two tape reels inside a cassette shell, with the two tape reels having a tape-shaped recording medium, such as a magnetic tape, wound thereupon.
There is a tape cassette comprising a reel lock mechanism for preventing rotation of the tape reels when the tape cassette is not loaded to a tape drive device. By this structure, when the tape cassette is not loaded, even if, for example, vibration is exerted upon the tape cassette, a magnetic tape is prevented from becoming slack caused by rotation of the tape reels.
FIGS. 1 and 2 and FIGS. 23 to 28 illustrate a tape cassette b including a related reel lock mechanism a. FIGS. 1 and 2 show the entire tape cassette b, and are also used to illustrate a first embodiment of the present invention described later. Of the symbols used, reference numerals are used to denote component parts used in the present invention, while lower-case alphabetical letters are used to denote component parts used in the related technology.
In the tape cassette b, two tape reels e and e upon which a magnetic tape d is wound are rotatably accommodated inside a cassette shell c. A plurality of engaging teeth f, f, . . . , serving as protrusions, are formed at the outer peripheral edge of a lower flange of each of the tape reels e and e, with recesses being formed therebetween (see FIGS. 25 to 28).
The reel lock mechanism a is provided in a substantially triangular space (hereinafter referred to as “the triangular space”), defined by the back wall and the two reels e and e, inside the cassette shell c. A rectangular hole g is formed in a portion of the bottom surface of the cassette shell c where the reel lock mechanism a is situated. When the tape cassette b is loaded into a tape drive device, an insertion pin h, provided at the tape drive device, is inserted into the cassette shell c from the rectangular hole g, and acts on the reel lock mechanism a in order to unlock the tape reels e and e (see FIGS. 25 to 28).
The reel lock mechanism a comprises a slider i, two lock portions j and j, a lock spring k, and a slide spring l (see FIGS. 23 and 24).
The slider i is supported so as to be movable forward and backward inside the triangular space. Upwardly protruding support shafts m and m, which are separated in the leftward and rightward directions, are provided at the back end of the slider i. A placement recess n, which opens upward and backward, is formed between the support shafts m and m of the slider i (see FIGS. 23 and 24).
A pin insertion recess o for inserting the insertion pin h of the tape drive device is formed in the bottom surface of a block situated forwardly of the placement recess n in the slider i, with the lower half of the back surface defining the pin insertion recess o being an inclined surface p which is displaced backward as it extends downward.
Lock portions j each comprise one plate member having a chevron shape as a whole in plan view. Cylindrical support portions q extending vertically are integrally formed with the back edges of their respective plate members. The front ends of the two lock portions j and j extend away from each other. Tapered anchoring pawls r and r are formed at the front ends of the respective lock portions j and j (see FIGS. 23 and 24).
Spring catch portions s are formed on the top side edges of the respective lock portions j between the support portions q and the respective anchoring pawls r. Lower side edges of the respective lock portions j have forms in which the front side portions thereof protrude downward from substantially the longitudinal centers of the respective lock portions j. The back edges of the respective downwardly protruding portions are cam followers t which come into contact with respective cams (described later) for rotating the respective lock portions j (see FIGS. 23 and 24).
Externally fitting the support portions q to their respective support shafts m of the slider i rotatably supports the lock portions j at the slider I (see FIGS. 23 and 24).
Anti-rotation portions are provided at the respective lock portions j, so that the angle of rotation in the direction in which they engage the engaging teeth f of the tape reels e does not become equal to or greater than a predetermined angle.
The lock spring k is a torsion coil spring, in which coil portions u and u, a linking portion v linking the coil portions u and u, and engaging portions w and w are integrally formed, with the coil portions u and u being separated in the leftward and rightward directions and the engaging portions w and w protruding from their respective coil portions u and u and being positioned outwardly of the linking portion v. The two coil portions u and u are supported at their respective support shafts m and m by being externally fitted to the top sides of the support portions q and q of their respective lock portions j and j. The two engaging portions w and w engage the spring catch portions s and s of the two lock portions j and j, so that the lock portions j and j are biased in the directions in which the anchoring pawls r and r move away from each other, that is, in the directions in which the anchoring pawls r and r engage the engaging teeth f and f of the respective tape reels e and e (see FIG. 24).
The slide spring l is a helical compression spring, and is provided in a compressed manner between the inside surface of the back wall of the cassette shell c and the placement recess n of the slider i. By this, the slider i is biased forward (see FIGS. 25 to 28).
Ribs x and x having small heights measured from the bottom surface are provided in a standing manner on both the left and right sides of the slider i inside the cassette shell c. In plan view, the ribs x and x comprise portions extending in the direction in which the slider i slides, portions which are one size larger than the outer peripheral edges of the respective tape reels e and e, and portions which are located in the paths of movement of the respective lock portions j and j. Of these portions, the portions located in the paths of movement of the respective lock portions j and j, more specifically, the portions situated in correspondence with the respective cam followers t and t are cams y and y for controlling rotation of the respective lock portions j and j (see FIGS. 23 and 24).
When the tape cassette b is not loaded to a tape drive device, the slider i is biased forward, and the cam followers t and t of the respective lock portions j and j are separated from the respective cams y and y, so that the anchoring pawls r and r at the front ends of the respective lock portions j and j are rotated in the directions in which they move away from each other, and engage an engaging tooth f and an engaging tooth f of the respective tape reels e and e, thereby locking the tape reels e and e (see FIG. 25). In other words, the tape reels e and e are prevented from rotating in the direction in which the magnetic tape d becomes slack.
Since the slider i is biased forward, a rotational force is applied to the two tape reels e and e through the respective anchoring pawls r and r in the direction in which the magnetic tape d is tensioned, so that the magnetic tape d is maintained in a tensioned state when the tape reels e and e are locked.
When the tape cassette b is loaded into a tape drive device, the insertion pin h of the tape drive device is inserted into the cassette shell c from the rectangular hole g of the cassette shell c, and comes into contact with the inclined surface p defining the pin insertion recess o of the slider i (see FIG. 26(B)).
When the insertion pin h is further inserted into the pin insertion recess o of the slider i, the front end of the insertion pin h pushes the inclined surface p, so that the slider i moves towards the back against the biasing force of the slide spring 1 (see FIG. 27).
The cam followers t and t of the respective lock portions j and j come into contact with the respective cams y and y, and move towards the back along the cams y and y, so that the lock portions j and j rotate in the direction in which the anchoring pawls r and r move towards each other. By this, the anchoring pawls r and r of the respective lock portions j and j move away from the respective tape reels e and e, so that the tape reels e and e are unlocked, and are brought into a rotatable state (see FIG. 28).
Next, FIGS. 1 and 2, FIGS. 14 to 17, and FIGS. 31 to 35 illustrate a tape cassette b including another related reel lock mechanism a′. This related reel lock mechanism a′ differs from the above-described related reel lock mechanism a only in the forms of the cam followers. These cam followers will be primarily described. Accordingly, the other corresponding parts to those of the reel lock mechanism a will be given the same reference numerals, and will not be described below. The overall form of this tape cassette b is substantially the same as the above-described tape cassette b. Accordingly, the reel lock mechanism illustrated in FIGS. 1 and 2 is labeled a′, and a general description thereof will not be given below.
FIGS. 14 to 17 are also used to illustrate a second embodiment of the present invention described later. Of the symbols used, reference numerals are used to denote the component parts used in the present invention, while lower-case alphabetical letters are used to denote the component parts used in the related technology. Of the forms of the component parts shown in FIGS. 14 and 15, the forms of anchoring pawls, which are front end portions of respective lock portions, are those used in the second embodiment of the present invention. The second embodiment differs from the related technology only in the forms of the anchoring pawis. The forms of the anchoring pawls, which are front end portions of respective lock portions, used in this different related technology are shown in FIGS. 31 to 35.
Spring catch portions s are integrally formed with the top edges of respective lock portions j between support portions q and respective anchoring pawls r (see FIGS. 14 and 15). Downwardly protruding pins are formed at the inner sides of the respective lock portions j situated towards the respective support portions q, that is, at the sides facing their respective other lock portions j. The pins are cam followers t′ which come into contact with the cams y for rotating the lock portions j (see FIGS. 31 to 35).
When the tape cassette b is loaded into a tape drive device, an insertion pin h of the tape drive device is inserted into a cassette shell c from a rectangular hole g of the cassette shell c, and comes into contact with an inclined surface p defining a pin insertion recess o of a slider i (see FIG. 26(B)).
When the insertion pin h is further inserted into the pin insertion recess o of the slider i, the front end of the insertion pin h pushes the inclined surface p, so that the slider i moves towards the back against the biasing force of the slide spring 1 (see FIG. 27).
The cam followers t′ and t′ of the respective lock portions j and j come into contact with the respective cams y and y, and move towards the back along the cams y and y, so that the lock portions j and j rotate in the direction in which the anchoring pawls r and r move towards each other. By this, the anchoring pawls r and r of the respective lock portions j and j move away from the respective tape reels e and e, so that the tape reels e and e are unlocked, and are brought into a rotatable state (see FIGS. 31 to 35).
FIGS. 31 to 35 are enlarged plan views showing states of the reel lock mechanism a′ in which a tape reel e changes from a locked state to an unlocked state.
The reel lock mechanisms a and a′ of the above-described related tape cassettes b have the following problems {circle around (1)} to {circle around (3)}.
{circle around (1)} The tape cassette b cannot be reduced in size.
{circle around (2)} The elastic force of the lock spring k cannot be made small, so that the tape reels cannot be stably locked.
{circle around (3)} When the tape reels e are unlocked, the tape reels e rotate in the direction in which the magnetic tape d is made slack, so that the magnetic tape d may become entangled with a member of the tape drive device.
First, problem {circle around (1)} will be explained with reference to the related reel lock mechanism a described earlier.
When the tape cassette b is made small, there is a problem in that the related reel lock mechanism a cannot be disposed in a small triangular space.
In other words, when the tape cassette b is reduced in size, the triangular space naturally becomes smaller, so that the sliding amount of the slider i becomes smaller. On the other hand, the amount of displacement of the anchoring pawls r and r of the respective lock portions j and j required to unlock the tape reels e and e (distance of movement of the anchoring pawls r and r away from the respective tape reels e and e) do not change very much even if the tape cassette b becomes smaller, so that the amount of displacement needs to be substantially the same as the amount of displacement of the anchoring pawls r and r of the related reel lock mechanism a.
Therefore, in order to make the amount of displacement of the anchoring pawls r the same regardless of a reduction in the sliding amount of the slider i, the pressure angles between the cams y and the respective cam followers t must be made large. When the pressure angles are increased, a large force needs to be exerted upon the cam followers t in order to rotate the respective lock portions j, so that the slider i and the lock portions j cannot move smoothly. As a result, stable locking and unlocking of the tape reels e cannot be performed.
The pressure angles are angles formed at portions of contact of the respective cams y and their respective cam followers t by normal lines T1 to the cams y and movement directions T2 of the cam followers t (directions of tangential lines to the cam followers t with respect to rotational centers O) (see FIGS. 29 and 30).
FIGS. 29 and 30 are schematic views for comparing the relationships between the pressure angles and the sliding amount of the slider i when the amount of displacement of the anchoring pawls r of their respective lock portions j is made constant.
FIG. 29 schematically shows the relationships in the related reel lock mechanism a, in which, when the sliding amount of the slider i is σ and the displacement amount of the anchoring pawls is δ, the pressure angles between the cams y and the corresponding cam followers t are α.
On the other hand, FIG. 30 shows the relationships in the reel lock mechanism where the sliding amount of the slider i is reduced due to a size reduction in the tape cassette b. Here, in the case where the sliding amount of the slider i is reduced to σ′, which is substantially half the sliding amount σ of the slider i shown in FIG. 29, when the displacement amount of the anchoring pawls r of the lock portions j are kept equal to the displacement amount δ, the pressure angles between the cams y and the respective cam followers t become α′.
Therefore, it can be understood that, when the sliding amount of the slider i becomes smaller due to a size reduction of the tape cassette b, the pressure angles between the cams y and the respective cam followers t become large (α′>α), so that the reel lock mechanism a either cannot move smoothly or cannot easily move smoothly.
Problem {circle around (2)} will be explained with reference to the related reel lock mechanism a. The lock portions j are supported by the slider i in a cantilever manner, so that, when they are subjected to shock, they tend to rotate with the support portions q as centers. Therefore, a larger force is required to keep the tape reels e in a locked state.
More specifically, the lock portions j of the reel lock mechanism a are supported at the support portions q at one end of the lock portions j by the support shafts m of the slider i. Therefore, in the case where the anchoring pawls r are engaged with and locked at an engaging tooth f and an engaging tooth f of the respective tape reels e, if a shock is exerted upon the lock portions j when, for example, the tape cassette b is dropped, the lock portions j try to rotate with the support portions q as centers. When the tape cassette b is dropped, a shock of 500 G to 1000 G is ordinarily exerted, so that a large rotational force is generated at the lock portions j supported in a cantilever manner.
Obviously, it is necessary to assume that the tape cassette b may be dropped at the time the tape cassette b is being designed. Thus, it is necessary to design the tape cassette b so that the lock spring k has a high elastic force in order to prevent the tape reels from becoming unlocked when the tape cassette b is dropped.
Therefore, the contact pressures between the cams y and the respective cam followers t become larger, so that repeated sliding causes serious wearing of the contact surfaces of the cams y and the respective cam followers t, thereby causing both contact surfaces to become rough. This results in the problem of making it more difficult to smoothly move the reel lock mechanism a.
In order to prevent this, for example, the pressure angles may be made smaller, or the coefficient of friction between the materials of the contact surfaces may be made smaller. However, the former goes against size reduction of the tape cassette b as mentioned above, and the latter results in increased costs, so that these cannot serve as solutions.
Problem {circle around (3)} is described with reference to the related reel lock mechanism a′. When the tape reels e are unlocked, the tape reels e rotate in the direction in which the magnetic tape d becomes slack, so that the portion of the magnetic tape d outside the cassette shell c becomes slack. Accordingly, after loading the tape cassette b into the tape drive device, the slack magnetic tape d may cause troubles such as the tape path not being properly formed or the magnetic tape d becoming entangled with a member of the tape drive device.
Each tape reel e is in a locked state when the front end of its anchoring pawl r is positioned at a corner of a recess f1 of each tape reel e situated at a side towards which each tape reel e winds up the magnetic tape d (this direction hereinafter referred to as “forward,” and the opposite direction hereinafter referred to as “backward” in terms of the tape reels 3) (see FIG. 31). In this state, when the slider i moves backward, each anchoring pawl r is caught by a protrusion f2 behind the adjacent recess f1 where the anchoring pawl r is positioned (in FIG. 32, the anchoring pawl r is shown as being caught by the protrusion f2 marked with a dot) (see FIG. 32). Further backward movement of the slider i causes each protrusion f2 which has caught its anchoring pawl r to move backward, so that each tape reel e rotates in the direction in which the magnetic tape d becomes slack (see FIG. 33).
Accordingly, the present invention makes it possible to overcome the above-described problems {circle around (1)} to {circle around (3)} in order to reduce the size of a tape cassette, to stabilize locking of a tape reel, to prevent reverse rotation of the tape reel when the tape reel is unlocked to minimize slacking in a magnetic tape.